An optical element used in optical equipment, for example, in a camera, a binocular telescope, a microscope, or a semiconductor exposure apparatus has been optionally provided with a black light-shielding film at an outside of the optically effective area to reduce stray light. This light-shielding film sufficiently absorbs stray light reached, for example, the edge of a lens to reduce unnecessary light such as flare and ghost.
This light-shielding film is expected to have an effect of reducing stray light entered in the light-shielding film from the inside of the optical element and an effect of reducing stray light entered in the light-shielding film from the air interface. That is, the light-shielding film is required to suitably reduce two types of reflected light called internal reflection and surface reflection.
Recently, along with a reduction in size and an improvement in performance of optical equipment, materials having higher refractive indices have been widely used in optical elements of optical systems. Specifically, for example, a glass material having a refractive index of 1.8 to 2.0 or higher than 2.0 is used. In order to reduce internal reflection of stray light entering into an optical element having a high refractive index, the light-shielding film needs to have a higher refractive index. Accordingly, for example, a material having a high refractive index is added to a light-shielding film to control the refractive index of the light-shielding film to a suitable level (PTLs 1 and 2).
PTL 1 discloses an internal reflection light-absorbing coating that prevents internal reflection by adding coal tar to the coating to increase the refractive index and also adding coal tar, carbon black, and a dye to the coating to absorb light. PTL 2 discloses an internal reflection-preventing coating for an optical member. The coating contains inorganic fine particles having a refractive index of 1.5 or more and a pigment.